1. Field of the Invention
The present invention relates to an image forming apparatus such a copier, a printer, a facsimile, etc and more particularly a sheet wrinkling supression image forming apparatus.
2. Discussion of the Background
Recently, an image forming apparatus employing an electro-photographic system is becoming more popular and is capable of forming images on various types of and sizes of sheets. In particular, an industrial image forming apparatus enables a user to copy on a polyester film and tracing paper which is a second master drawing in addition to a plain paper. Further, the industrial image forming apparatus occasionally utilizes a sheet larger than A0 size (JIS).
Many exemplary electro-photographic systems include a fixing station formed from a pair of heat and pressure applying rollers. However, an entire width of a tracing paper having weak rigidity is difficult to uniformly enter into a nip formed between the heat and pressure applying rollers. As a result, an amount of transportation deviation between widthwise left and right sides increases, and accordingly wrinkling easily arises. In the worst situation, the wrinkling occasionally reaches and affects a contacting portion (i.e., a transfer area) of the sheet that contacts a photo-conductive (PC) member located upstream.
Preventing such sheet wrinkling in the fixing station together with defective transfer is disclosed in Japanese Patent Laid Open No. 5-224548. Specifically, when a sheet carrying an image transferred from a PC member is conveyed by a void conveying apparatus to a nip formed between heat and pressure applying rollers, the void conveying apparatus is controlled to lose its conveyance force so that a tension can accordingly be applied to the sheet between the fixing station and void conveying apparatus. As a result, wrinkling of the sheet is avoided in the fixing station.
However, the inventor of the present invention realized a sensor for detecting passage of the sheet and for generating a detection signal on a sheet conveyance path in order to recognize a timing when the sheet is conveyed into the nip between heat and pressure applying rollers may be included. In addition, since a transfer and conveyance apparatus including the void conveyance apparatus is disposed between a pair of the heat and pressure applying rollers and PC member, the configuration is relatively complex and undesired cost increases occur. Further, a counter measure configured to minimize wrinkling caused by a difference in a sheet type is desired.
Accordingly, an object of the present invention is to address and to resolve the above-noted and other problems and provide a novel image forming apparatus.
The above and other objects are achieved according to the present invention by providing a novel image forming apparatus including a sheet feeding section for feeding a sheet, and a sheet transportation path defining a transportation path for the sheet fed from the sheet feeding section. An image formation section including a photo-conductive member arranged in the sheet transportation path may also be provided so as to form an image. A fixing section may be provided so as to fix a toner image transferred onto the sheet from the photo-conductive member with heat and pressure rollers, and a sheet type recognition device may be provided so as to set information related to a sheet type selected by an operator. A sheet linear velocity control device may also be provided so as to only change a sheet linear velocity of the feeding section in accordance with the sheet type.
In another embodiment, the sheet feeding section is driven by a separately employed motor, and sheet transportation series members including the photo-conductive member arranged on the sheet transportation path are driven by a commonly used motor.
In yet another embodiment, the sheet feeding linear velocity control device decreases a linear velocity of the sheet feeding section when a weak rigidity sheet is selected and set.
In still another embodiment, the sheet feeding linear velocity control device gradually increases and approximates the decreased linear velocity of the sheet feeding section to the previous linear velocity when a sheet length exceeds a prescribed value.